Number of ways to place 4 nonattacking knights on an n X n board.

Terms

a(0) =0a(1) =1a(2) =18a(3) =412a(4) =4436a(5) =26133a(6) =111066a(7) =376560a(8) =1080942a(9) =2732909a(10) =6253408a(11) =13204356a(12) =26100160a(13) =48819677a(14) =87137934a(15) =149398608a(16) =247349946a(17) =397168485a(18) =620696612a(19) =946921684a(20) =1413726108a(21) =2069939461a(22) =2977725410a(23) =4215337872